A capacitor is charged with a battery and then its plate separation isincreased without disconnecting the battery. What will be the change in 1) Charge stored in the capacitor 2) Energy stored in the capacitor 3) Potential difference across the plates of the capacitor 4) Electric field between the plates of the capacitor.

Since the battery is not disconnected, the voltage across the plates remain same and equal to that provided by battery,

Due to separation of plates, the capacitance of the capacitor decreases.
Hence the charge stored=decreases.
Energy stored in capacitor=decreases.
Potential difference across the plates remains the same
Electric field =decreases.